The spine is a generally flexible column that can take tensile and compressive loads, allows bending motion and provides a place of attachment for ribs, muscles and ligaments. Generally, the spine is divided into three sections: the cervical, the thoracic and the lumbar spine. FIG. 1 illustrates schematically the lumbar spinal 1 and the sacrum regions 3 of a healthy, human spinal column. The sections of the spine are made up of individual bones called vertebrae, and the vertebrae are separated by intervertebral discs which are situated therebetween.
FIG. 2 illustrates a portion of the right side of a lumbar spinal region with a damaged intervertebral disc 5 disposed between two adjacent vertebrae 7, 9. The lumbar spinal region includes an anterior section 11 and a posterior section 13. In any given joint, the top vertebra may be referred to as the superior vertebra and the bottom one as the inferior vertebra. Each vertebra comprises a generally cylindrical body 7a, 9a, which is the primary weight bearing area of the vertebrae 7, 9, respectively. Vertebra 7 further includes a spinous process 7b and transverse processes 7c, 7d (7b and 7c are visible, for example, in FIGS. 2-3 and 7d is visible, for example, in FIG. 3). Similarly, the vertebra 9 includes a spinous process 9b and transverse processes 9c, 9d (not shown). The processes, among other functions, provide areas for muscle and ligament attachment. A facet joint 7e is located between articular processes 7f, 9f of the superior and inferior vertebrae 7, 9, respectively.
Intervertebral discs function as shock absorbers and as joints. They are designed to absorb the compressive and tensile loads to which the spinal column may be subjected while at the same time allowing adjacent vertebral bodies to move relative to each other a limited amount, particularly during bending (flexure) of the spine. Thus, the intervertebral discs are under constant muscular and/or gravitational pressure and generally are the first parts of the lumbar spine to show signs of “wear and tear”.
Facet joint degeneration is also common because the facet joints are in almost constant motion with the spine. In fact, facet joint degeneration and disc degeneration frequently occur together. Generally, although one may be the primary problem while the other is a secondary problem resulting from the altered mechanics of the spine, by the time surgical options are considered, both facet joint degeneration and disc degeneration typically have occurred. For example, the altered mechanics of the facet joints and/or intervertebral disc may cause spinal stenosis, degenerative spondylolisthesis, and degenerative scoliosis.
One surgical procedure for treating these conditions is spinal arthrodesis (i.e., spine fusion), which has been performed both anteriorly and/or posteriorly. The posterior procedures include in-situ fusion, posterior lateral instrumented fusion, transforaminal lumbar interbody fusion (“TLIF”) and posterior lumbar interbody fusion (“PLIF”). Solidly fusing a spinal segment to eliminate any motion at that level may alleviate the immediate symptoms, but may result in further deterioration of the adjacent levels over time. Maintaining motion at the joint, for example through the use of an artificial disc, may be a solution of some patients. However, none of the known devices or methods provide the advantages of the embodiments of the present disclosure.
Accordingly, the foregoing shows there is a need for improved spinal arthroplasty devices that avoid the drawbacks and disadvantages of the known implants.